Hello again Hambers ! Was just talking about engine (SBC) breathers . So a guy was telling me that it's OK to have (3) breathers on my SBC , it might cause some oil spray on engine but the engine won't be harmed. In reality I think it's only (2) breathers ,I got the oval finned ones on each finned valve cover ( 1 being PCV valve the other a breather & it's a pre86 SBC so it's got the intake oil fill tube with finned fill/breather cap .Another chimed in to say you shouldn't have so many because it will screw up crank case psi .This is probly wasting alot of your time if you got this far . But just wondering thoughts .I'm fucking bored with this engine ,I want something more radical .
Damn ,that things breathing more than mine for sure! Lol. Never saw breathers on valve covers like that.
That's what I was told ,that its good for it to breath & if possible put them at different corners for flow through ( which I'm not sure about , but ....) . I mean I see some engines with valve covers with NO breathers So....
A proper PCV system is probably your best bet. Like the Pope says not both. Early Chevrolets had a breather on the fill tube and road draft tube in the rear. Fresh air in and crank case vapor out. Lots of threads on this.
really? I thought that's how it's supposed to be...that's how almost every engine I've built was set up. Except the ones that still had draft tubes instead of PCV. The one exception I have uses PCV on one valve cover, and a header evac on the other. It actually draws a vacuum in the crank case under some conditions. It also uses the least oil of just about any old engine I've ever had.
What confuses a lot of people on the subject is there is a "fresh air side" listed in writings on pcvs. People think it means a breather. In actuality it's supposed to hook to your air filter. Air going into the carb creates a draw that provides suction to keep the pcv valve closed until there's positive crankcase pressure caused by blowby etc that will push the pcv valve open and allow the vacuum hose to draw it out till pressure is equalized and valve closes again. Likely the reason why the one you mentioned with the header evac uses less oil is the draw you mentioned. With a pcv and a breather you basically have a slightly restricted vacuum leak.
There are two class of pcv systems the first one uses a vent to the outside pulling gases through the PCV . These work well at an idle ( high) vacuum second design the vent tube went to the air cleaner for under load (low vacuum) when air is rushing into the carburetor pulling some of the blowby gasses with it.
On most all street sbc's I build they have a pcv and a breather. I understand the argument of the tube to the air cleaner factory set up but also Chevrolet ran that set up on open element Corvettes and Z28s and the pressure change would be negligible between that and a valve cover breather.
Typical stock V-8 runs a pcv on one valve cover, and a hose from opposite side cover to air cleaner with a vent or draw filter inside air filter housing. A chrome breather instead of hose to air cleaner will be fine.
I remember there were variations on the theme. Some had the valve on the filler tube some on the valve cover. The filtered fresh air came from the air cleaner base connected to the rear port where the draft tube was or the opposite valve cover. Some got vacuum from the base of the carb or intake. I think there were different valves depending on the vacuum signal ((i.e. engine application).
Closed PCV systems have a tube to the air cleaner. But it's outside the filter element, and not likely to be at significantly different pressure than atmospheric. CPCV started late 60s, didn't it? There were a lot of engines built with a breather cap, not an air cleaner vent, for the the "fresh air side" of the crankcase vent system.
In my experience an improperly vented engine either blows oil out of its seals or gaskets or sucks oil through an improperly shielded pcv valve.
On my race car I let it out to atmosphere, I don't want to pollute my A/F charge going into my engine. For a street car and proper pollution control it should be recirculated back to the engines intake system. It all went down hill from there with the EGR and other systems.
Take the lid off your air cleaner and start the engine. Next hold a dollar bill by the end and see how close you get to the carb throat before it starts trying to suck the bill to the carb
Does not take much suction by the fresh air tube to keep the pcv shut. Reason guys get away with breather caps. And with the fresh air side it's more of a siphon effect than vacuum.....like on a siphon feed paint gun
A little like Dennys (above) - Here's my 383 for a Studebaker hot rod. And NO...you can't have too much crankcase breathing !! The old Studebaker R3, R4 Avanti engines had three. One in each rocker cover AND one in the oil pan. Whoever made the comment about the "crankcase" pressure was on good drugs... What would he say about todays "vacuum pumps" that actually pull...a VACUUM in the crankcase ! Hell here's one on a flathead oil pan. You can use as many breathers as you like, and put them where...you like. Mike
Wow really learned alot & glad this discussion opened up . My one breather is on one valve cover the other ( breather looking PCV valve ) has the hose going to the back of my QUICKFUEL carb .So air is being drawn into intake from vacuum of intake air .And the oil fill/ breather is allowing air to flow in I guess mostly because I have no oil mist . I do have or had valve cover oil leak that I thought was because of the breather set up ,but more homework showed SBC have problems with valve cover sealing ( WHICH is another can of worms for other threads ) I got that worked out .But thanks for the insight on my question , you guys AGAIN have helped me understand more than I did before !! THANKS BROTHERS!!
I've always used these gaskets to solve sbc valve cover leaks. https://www.felpro.com/parts/performance/valve-cover-gaskets.html
The PCV valve doesn’t work like that, whether the tube leads to the air cleaner or not has no effect on the operation of the PCV valve. The valve’s function is to limit the flow through it to a set level irrespective of manifold vaccum it only closes in the case of a back fire or when the engine is not running.
The PCV valve uses the engine's vacuum to pull air through the crankcase and reintroduce it back into the intake manifold system. LINK : PCV Valves - Crankcase Ventilation System - Machinery Lubrication that's what Google I shows on : How PCV valve works . Sounds like it keeps psi equal by cycling air to me .
It allows flow, but not enough flow to equalize pressure....if it did, the engine would have no vacuum at all. hint: the cross sectional area of the PCV opening is way smaller than that of the throttle bores
Thanks 05snopro440 , yes I used the blue silicone ones still leaked ,went back to cork with a litte sealant .I'm using no name finned covers with aluminum edelbrock heads ( should a used edelbrock covers/ gaskets . But it sealed . Squirrel , I hear ya ,the typical PCV hole is small .And they have the filter too on some if not all . THANKS !
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